Smoking is known as an important risk factor of many diseases which are the leading causes of human death. The major disease caused by smoking include lung cancer, chronic obstructive pulmonary disease (COPD), coronary artery disease, cerebrovascular disease such as stroke, heart failure, circulatory disease, laryngopharyngeal cancer, oral cancer, etc.
Cigarette smoke contains over 4,000 toxic substances, including carcinogens. Among them, tar which is a mixture of several toxic substances and nicotine are known as important harmful ingredients. Since the harmful ingredients contained in tobacco suppress SIRT1 which is known as human longevity gene, they render cigarette smokers vulnerable to inflammations or severe diseases such as chronic obstructive pulmonary disease (COPD). Also, smoking is known to cause abnormality in mitochondrial function.
Owing to the change in lifestyles with industrial development and surplus high-calorie food, humankind is exposed to the risk of metabolic diseases represented by obesity, type 2 diabetes, hyperlipidemia, fatty liver, etc. Considering that, among them, obesity is the major cause of metabolic diseases such as type 2 diabetes, hyperlipidemia and fatty liver, the other metabolic diseases could be prevented by preventing or improving obesity.
Obesity is most commonly caused by energy input exceeding consumption of energy by the body. Specifically, surplus energy is stored in adipose tissue in the form of triglyceride. Although the adipose tissue can store a large amount of surplus energy as if a rubber balloon, the size of adipocytes is increased at the same time. In addition, if the amount of surplus energy to be stored exceeds the capacity of the adipose tissue, lipid dysregulation lipotoxicity occur in which energy is stored in other tissues such as muscle, liver, etc. The fat stored in each tissue is changed into free fatty acid through lipolysis. The free fatty acid is known to inhibit insulin signaling through signaling mechanisms involving JNK, PKC, etc. The inhibition of insulin signaling necessarily induces insulin resistance and, as a result, leads to various metabolic diseases such as hyperglycemia, hyperlipidemia, hypercholesterolemia, type 2 diabetes, fatty liver, etc. As such, obesity is a severe problem since it is not just an appearance concern but is accompanied by various adult diseases.
The retina is an organ considered part of the central nervous system. Fully grown retinal cells do not normally divide like most neurons existing in the brain. Therefore, if the function of the retinal cells is degenerated, disorder can occur easily in tissue or organ level when compared with other system and, as a result, aging proceeds fast. Oxidative stress is a major cause of the degeneration of the retinal cell function because the retina, optic nerve, photoreceptor cells and lens constituting eyes are consistently exposed to the cause of oxidative damage such as light and UV. Upon oxidative damage, mitochondrial DNA in intraocular cells is damaged. Since mitochondria lack enzymes that can repair the damaged DNA, the damaged mitochondrial DNA is accumulated in the cells with time. If the mitochondrial DNA becomes unstable, modification occurs in mitochondria protein synthesized therefrom. As a result, the mitochondrial membrane potential decreases, followed by decreased production of mitochondrial energy (ATP) and relatively increased generation of reactive oxygen species. Consequently, modification occurs in the DNA, protein and lipid constituting the cells and aging of eyes or eye disease such as macular degeneration, uveitis, glaucoma, diabetic retinopathy and cataract occurs. Accordingly, eye disease can be prevented or improved by inhibiting destabilization of mitochondrial DNA. However, the most widely known method of delaying eye aging at present is an indirect method of using antioxidant to reduce oxidative stress.
When the human body is invaded by viruses, bacteria, etc., the infected cells produce histamine, kinin, etc., which dilate capillaries of the damaged part and thus allow various immune cells including macrophages and killer cells to easily reach the wound site. After the immune cells such as macrophages engulf the invading viruses, bacteria, etc., various enzymes in lysosomes break them down and the immune response is terminated.
Immune response is an essential for maintenance of the body's homeostasis along with energy metabolism. Innate immunity is a primary defense mechanism against nonspecific sources of infection from outside and defends our bodies from incessant invasion from outside through inflammatory responses. The inflammatory responses are strictly regulated because they have a great impact on cells and tissues. If the inflammatory response is not controlled normally, various immune diseases such as hay fever, rheumatoid arthritis, allergy, atopic dermatitis, etc. can occur. Moreover, since chronic inflammation wherein the expression of inflammation-related genes is increased even in the absence of external pathogens can cause metabolic diseases such as type 2 diabetes by affecting insulin resistance, the regulation of immune response is a prerequisite for the control of homeostasis of individuals.